In an optical disk device using an exchangeable disk-like optically recording medium such as an optical magnetic disk (called optical disk herein after) as a recording medium, the mark edge recording method (mark length recording method) has been used as a method of recording data in high density.
In this mark edge recording method, for instance, as shown in FIGS. 13 (a) to (c), after data to be recorded is modulated according to the RLL (1, 7, 2, 3) modulation rules, a record signal (record pulse) is formed by applying the NRZI modulating method to the modulate data to be recorded, and a record mark corresponding to the record signal is formed in an optical disk by driving a semiconductor laser element in an optical pick-up device according to the record signal, thus the data being recorded.
Also a regenerative signal obtained by regenerating the record mark (Refer to FIG. 13 (d)) is converted to a binary coded pulse (Refer to FIG. 13 (e)) by subjecting the signal to a binary-coding with a specified threshold value, and the data to be recorded is regenerated according to a position of an edge position of this binary-coded pulse.
By the way, an optical disk mounted on an optical disk differs in terms of its material, for instance, according to the manufacturer, so that the thermal conductivity is dispersed to some extent in (for instance, rated) tolerance. Also the same type of optical disk from the same manufacture may differ in terms of the thermal conductivity to some extent.
Thus the thermal conductivity of each optical disk is heterogeneous, so that sometimes the troubles as described below occur.
Namely, as shown in FIG. 14 (a), when a record pulse having a certain pulse width is loaded to a semiconductor laser element, a record mark MKa as shown in FIG. 14 (b) is formed in an optical disk having a small thermal conductivity, while a record mark MKb as shown in FIG. 14 (c) is formed in an optical disk having a large thermal conductivity.
Herein, when the thermal conductivity is large, a range heated by a laser beam spot becomes larger as compared to that when the thermal conductivity is small, so that the length LB of the record mark MKb become larger than that of the record mark MKa, and as a result the mark edge can not be detected correctly when the data is regenerated, which sometimes causes a data error.
For this reason, to solve the trouble as described above, for instance, as shown in FIG. 15 (a) to FIG. 15 (c), a system has been proposed in which a corrected record pulse having a reduced pulse width is formed and a length of a record mark is adjusted to an appropriate a value by using the corrected record pulse to record the data.
In the conventional type of device as described above, however, a length of a record mark can be adjusted to a value near the theoretical value in particular types of optical disk, but it is impossible in some types of optical disk, data error can not be eliminated.